ICQM Faculty member publishes an article in Nano Letters reporting dynamical evolution of anisotropic response in black phosphorus under ultrafast photoexcitation

As a bridge 2D material between graphene and transition metal dichalcogenide in terms of mobility and bandgap opening, black phosphorus (BP) has recently emerged as a promising material for high performance angle sensitive electronic and optoelectronic device for its high mobility and anisotropic electronic properties. Toward the application of BP in this direction, dynamical evolution of photo excited carriers and its induced transient change of anisotropic electronic properties are highly desired, but remain to be explored.

In the newly published paper “Dynamical Evolution of Anisotropic Response in Black Phosphorus under Ultrafast Photoexcitation”, Prof. Dong Sun’s experimental ultrafast spectroscopy group in collaboration with Prof. Ji Feng’s theoretic group have studied the dynamical evolution of anisotropic properties of black phosphorus under photo excitation using the angle-resolved transient reflection spectroscopy. The sample is provided by Professor Shuang Jia’s group, also affiliated with ICQM. The results show that conductivity ellipse of BP is stretched due to photoexcitation of hot carriers which implies BP becomes more anisotropic under photo excitation and relax isotropically thereafter. These results implies enhanced anisotropic performance of BP in high speed, high field electronic and optoelectronic devices. Furthermore, a two band model simulation by Professor Ji Feng’s group generally supports the observed dynamical enhancement of anisotropy, showing consistence between experiment and theory.

This work provides interesting device physics toward understanding angle sensitive operation behavior of various BP based electronic devices under high field working environment or optoelectronic devices when light illumination is involved. The paper has been published online on June 3, 2015: http://dx.doi.org/10.1021/acs.nanolett.5b01409.  Shaofeng Ge, a Ph.D student from Prof. Dong Sun’s group is the first author and Professor Dong Sun and Ji Feng share the corresponding author of this paper.

This project has been supported by the National Basic Research Program of China, the National Natural Science Foundation of China, Beijing Natural Science Foundation and the Specialized Research Fund for the Doctoral Program of Higher Education of China.

Figure (a) Schematic diagram of polarization resolved transient reflection experiment. (b) Probe polarization dependence of transient reflection spectrum (upper figure) and the spectra with different probe polarization at fixed delays (lower figure). (c) Dynamical evolution of Re (σ) ellipse at different delays. ΔRe (σ) is doubled for clarity. Inset: Enlarged plot of area marked by red rectangle.